1. Field of the Invention
The present invention relates generally to medical devices and medical methods. In particular, the present invention relates to systems, kits, and techniques for establishing percutaneous vascular access.
Access to patient blood vessels is necessary for a wide variety of diagnostic and therapeutic purposes. For example, intravascular catheters are introduced to both the arterial vasculature and the venous vasculature, typically using either surgical cut down techniques or percutaneous introduction techniques. Of particular interest to the present invention, the most common percutaneous introduction technique is referred to as the Seldinger technique. While a wide variety of variations exist, the basic Seldinger technique relies on initially accessing a target blood vessel with a needle. A guidewire is then passed through the needle into the blood vessel, and the needle withdrawn over the guidewire. A dilator is then passed over a guidewire to enlarge the diameter of the tissue tract so that it can accommodate a larger introducer sheath. Once the introducer sheath is in place, access to the blood vessel can be reliably obtained through a lumen of the sheath.
With the introduction of a greater number and variety of intravascular techniques, including angioplasty, atherectomy, endovascular aneurysm repair, minimally invasive cardiac surgery, and the like, a need has arisen to provide relatively large diameter access to the vasculature. Thus, access sheaths having a diameter of 24 French (8 mm) or greater are now commonly introduced using the Seldinger or other percutaneous techniques. As the number and size of procedures increase, so does the risk of complications which place individual patients at risk and which are costly to the healthcare system.
As larger and larger access diameters are sought, the need to dilate the tissue tract becomes greater. The use of conventional dilators, however, can significantly traumatize the skin. In particular, advancement of a conventional dilator through a tissue tract exerts significant axial forces on the tissue, potentially causing injury and delamination of adjacent tissue layers.
For these reasons, it would be desirable to provide improved systems, kits, and methods for establishing percutaneous vascular access for catheterization and other vascular procedures. In particular, it would be desirable to provide vascular access techniques which could dilate a percutaneous tissue tract with minimum trauma to tissue surrounding the tract. Such techniques should be suitable for forming large (as well as small) diameter access channels, typically having diameters as large as 6 mm, preferably as large as 8 mm, or larger. It would be still further desirable if the improved systems, kits, and methods would require little modification of existing techniques and systems for establishing vascular access. At least some of these objectives will be met by the inventions described hereinafter.
2. Description of the Background Art
The use of radially expanding dilators for accessing non-vascular body locations is described in U.S. Pat. Nos. 5,814,058; 5,431,676, 5,183,464, and copending application Ser. No. 08/424,696, all of which are commonly assigned with the present application and the full disclosures of which are incorporated herein by reference. U.S. Pat. No. 5,230,705, describes use of a needle disposed within a dilation structure for use in intravenous catheterization. See also U.S. Pat. Nos. 5,312,417; 5,246,424; 5,201,756, 5,139,511, and 4,899,729.
The present invention provides improved systems, kits, and methods for establishing percutaneous access to a patient""s vasculature. Access can be established to a variety of particular blood vessels, including both arteries and veins, such as the femoral artery, radial artery, and the like. The purpose for accessing the vasculature can be diagnostic, such as angiography, intravascular ultrasound, cardiac mapping, or the like, or can be therapeutic, such as angioplasty, atherectomy, minimally invasive cardiac surgeries, endovascular aneurysm repair, cardiac ablation, or the like.
The methods of the present invention comprise particular improvements over the Seldinger technique, as described above, employing a sheath dilator for expanding an initial needle penetration to a target blood vessel. As set forth in the Background section, use of a dilator/sheath assembly directly within a tissue tract can subject the tissue to significant axial forces which can delaminate or otherwise damage the tissue surrounding the tissue tract. The present invention reduces the risk of injuring the tissue by introducing a radially expandable sleeve over a guidewire which has been placed through the tissue tract using otherwise conventional techniques. The radially expandable sleeve will be immobilized (typically being manually held) relative to the tissue tract so that axial advancement of a sheath/dilator or other dilating member through the radially expandable sleeve will impart little or no axial force to the underlying tissue. Instead, only radially expansive forces will be transmitted outwardly through the sleeve.
Systems according to the present invention for establishing vascular access over a guidewire comprise a dilator and a radially expandable sleeve. The dilator has a lumen sized to be introduced over the guidewire. The guidewire will have a pre-selected diameter which is generally constant over its entire length. The diameter will be relatively small, typically being either 0.36 mm (0.014 in.) or 0.89 mm (0.035 in.), which are conventional sizes for guidewires used for vascular access. The lumen of the dilator will be sized slightly greater than the outside diameter of the guidewire with which it is to be used, typically being 0.46 mm (0.018 in.) or 1 mm (0.4 in.) for each of the guidewire sizes mentioned above. The dilator will have an outside diameter selected to provide for a desired degree of radial expansion of the tissue tract. Typically, the outside diameter of the dilator will be in the range from 1 mm to 2.5 mm for the smaller guidewire size and 1.3 mm to 3.3 mm for the larger guidewire size.
The radially expandable sleeve will have a lumen therethrough and an unexpanded diameter which is only slightly greater than the diameter of the associated guidewire, e.g., 0.41 mm (0.016 in.) for the 0.36 mm (0.014 in.) guidewire and 0.96 mm (0.038 in.) for the 0.89 mm (0.035 in.) guidewire. Typically, the sleeve will have an outside diameter which is no more than 300% of the guidewire diameter, preferably being no more than 200% of the guidewire diameter. The sleeve, however, will have an expandable outer wall which permits the dilator to be introduced over the guidewire and through the sleeve to cause expansion. In a first embodiment, the outer wall of the radially expandable sleeve can be compliant or elastic so that its cross-section collapses after expansion if the dilator used for expansion is withdrawn. Typically, the compliant or elastic structure will be reinforced with a tubular braid, e.g., a braid formed as a mesh of non-elastic filaments where radial expansion will cause axial shortening of the braid. The braid may be embedded in the elastic or compliant layer or may be covered by the elastic or compliant layer.
Alternatively, the radially expandable sleeve may have a plastically deformable body or may comprise a locking structure so that it retains its expanded diameter after dilation. Typically, the plastically deformable radially expandable sleeves will also be reinforced with the braid. For example, the braid may be covered or impregnated with a suitable plastically deformable material, such as expanded PTFE, irradiated polyesters, and the like. As an alternative or an addition to use of the plastically deformable sleeve matrix, the braid reinforcement may be configured so that the braid filaments interlock upon radial expansion. Thus, the filaments in themselves will resist radial collapse after the sleeve has been expanded.
When the system employs an elastic or compliant radially expandable sleeve, it will be necessary to provide further system component(s) to retain the sleeve in its expanded configuration after the dilator has effected dilation. Conveniently, this can be accomplished using a conventional sheath/dilator assembly as the dilator. After the sleeve has been expanded (thus expanding the tissue tract), an inner portion of the assembly, usually referred to as the dilator, can be withdrawn from the sheath, leaving the sheath in place to maintain the expanded diameter of the tissue tract. While this is an effective approach and utilizes a device with which the treating physician is quite familiar, it has the disadvantage that the radially expandable sleeve adds a very small thickness to the diameter to which the tissue tract is expanded. Use of the plastically deformable or locking sleeve will, in contrast, allow use of a simple dilator, i.e., one without an associated sheath. Thus, there will be no additional structure and no need to dilate the tissue tract any more than would be required with a conventional sheath dilator.
Optionally, the system may further comprise a sleeve introducer adapted to facilitate introduction of the sleeve over a guidewire through the tissue tract. In some patients, conventional Seldinger and other access techniques can be difficult due to the presence of scar tissue or other complicating factors. In such cases, significant pushing force may be required to advance the sleeve over the guidewire. While the small profile of the introducer sleeve reduces the force necessary for introduction over the guidewire, in some cases it will be desirable to still further reduce the introduction force. Such a reduction in introduction force can be accomplished by providing a tapered distal tip on the sleeve. While this could be done by modifying the design of the sleeve itself, it is more easily accomplished using a separate introducer sleeve having a tapered distal end a lumen therethrough. The sleeve is configured to receive a guidewire through its lumen and to be received within the lumen of the radially expandable sleeve. By then placing the radially expandable sleeve over the sleeve introducer, the temporary assembly of the sleeve and sleeve introducer can be introduced over the guidewire so that the tapered end of the sleeve introducer first advances through and dilates the tissue tract to reduce the necessary introduction force. After the distal end of the assembly reaches the blood vessel, the dilator may then be introduced over the assembly, i.e., the lumen of the dilator will pass over the exterior of the sleeve introducer. After dilation of the radially expansible sleeve is accomplished, the sleeve introducer and guidewire can then be removed from the expanded access channel defined by the dilator.
Methods according to the present invention for establishing vascular access comprise forming a percutaneous tissue tract to a target blood vessel. Typically, the tissue tract is initially formed using a needle and guidewire according to conventional techniques, such as the first steps in a Seldinger access protocol. A guidewire is positioned in the tissue tract, and a radially expandable sleeve positioned over the guidewire and through the tissue tract so that a distal end of the sleeve lies in the blood vessel. A proximal end of the sleeve will remain outside the tissue tract, and the sleeve may then be expanded from a narrow diameter configuration to a larger diameter configuration to provide an access lumen to the blood vessel. In a first embodiment, the sleeve will be plastically deformable or otherwise capable of maintaining its larger diameter configuration, and expansion can be effected using a simple dilator without an associated sheath. In an alternative embodiment, the radially expandable sleeve will be elastic or compliant and expansion can be effected using a sheath dilator where the dilator is removed after expansion and the sheath left in place to maintain the desired access lumen. Usually, the radially expandable sleeve which is advanced over the guidewire will have an outer diameter which is no more than 300% larger than the guidewire diameter, preferably no more than 200% larger.
The present invention still further provides kits for performing any of the methods described herein. The kits will comprise at least a radially expandable sleeve together with instructions setting forth a method according to the present invention. Usually, the kits will further comprise a dilator and optionally still further comprise a guidewire. The dilator may be a simple dilator with no associated access sheath when the radially expandable sleeve is plastically deformable or otherwise capable of maintaining its expanded diameter configuration. Alternatively, the dilator can be a conventional sheath/dilator combination when the radially expandable sleeve is elastic or compliant.